Engine analyzer



March 27, i956 J. l.. MINTO ENGINE ANALYZER 3 Sheets-Sheet l Filed May5l, 1950 AVVENTO 3 Sheets-Sheet 2 Filed May 3l, 1950 CATHODE VOLTAGE OFDIODE 46 IN V EN TOR. M

March 27, 1956 J, L NUN-ro A 2,740,069

I ENGINE ANALYZER Filed May 31, 1950 .'5 Sheets-Sheet 3 LOW PRIMARYVOLTAGE GOOD COMPRESSION sooTED LU GAPToo IDE wEAK sPARK AT PLUG PLUGsooTED No sPARK AT PLUG NORMAL TRACE NORMAL TRACE FAULTY coDsR I NoRALTRACE soo R.P.M. |200 R.P.M.

INVEN TOR.

MAQ/Af;

NORMAL TRACE Y FULT DlTlToR ENGINE ANALYZER John L. Ildinto, Marblehead,lv/Iass., assignor, by mesne assignments, to North Shore News Company,lLyrnt, Mass., a corporation of Massachusetts Application May 31, i959,Serial No. 165,362

9 Claims. (Cl. SiS-22) This invention relates principally to an internalcombustion engine analyser of the type which produces a visualindication on a cathode ray tube of the functioning and condition of theelectrical ignition system, and from such indication, through theapplication of known physical phenomena and laws, provides a basis forevaluating the over-all and specific performance of said engine. Thoughthe instrument has other applications, it is especially adapted for usein connection with evaluating performance and diagnosing mal-functioningof conventional internal combusion engines. 1t may be readily attachedto any electrically-fired internal combustion engine for simultaneouslychecking the performance of various components, particularly electrical,compression and mixture components, while in their normal place andduring operating conditions, either in shop tests or road tests.

Heretofore in order to test such various components, of any automobile,boat or other internal combustionengined device, it has been necessaryfor a mechanic first to remove them from the engine and place them in abench-testing device which, however, does not fully simulate engineoperating conditions, and, in no case checks such components whilefunctioning in place. Moreover, such checking has not evaluatedcompression conditions.

By the present invention, the various electrical components of anelectrically-fired internal combustion engine can be tested in actualoperation, without removing them from the engine, by a simple circuitconnection from my device to the ignition system to be tested, anddifferent sorts of defects can be ascertained in the ignition system,such as defective spark plugs, coils, or condensers, as well as certainfaulty compression and mixture conditions.

In general, the principle upon which the invention operates is by theapplication of a voltage rise in the ignition system, such as that at aspark plug prior to the occurrence of the spark, to a trigger circuit togenerate a saw-tooth sweep pulse forV application to the horizontal beamdeflection plates of a cathode ray tube to provide a horizontal timebase. At the same time, signals from the ignition system, either fromthe high voltage secondary or the low voltage primary of the ignitionsystem, are applied to a vertical beam deecting plate of the cathode raytube so the signals, corresponding, for example to the spark plugdischarges, are' shown for evaluation on the screen of the cathode raytube.

The usual type of cathode ray tube synchroscope, in which each separateinput pulse produces a separate sawtooth sweep pulse, is quiteunsuitable for use as an engine analyser, since present day ignitionsystems do not produce merely one voltage rise for each discharge of thespark plug under examination. Many other voltage rises are present whichare greater in amplitude than the voltage rise necessary to produce asaw-tooth sweep pulse for application to the horizontal plates of thecathode ray tube synchroscope. These impulses arise from two sources:(l)A under certain conditions the spark'` at the 2,740,0ss PatentedMar.` 27, 1956 l2 plug may be extinguished some k60 to 70 microsecondsafter the spark rst occurred, and be re-estblished some 20 to 30microseconds later; (2) with the higher compression and Wider plug gaps*in use in modern engines, radiation from one plug lead to another isquite frequently suicient to cause cross-firing of the engine.` `It isobvious that a voltage rise induced in the lead to the plug underexamination sullicient to produce a spark at that plug will also besufficient to produce, with the usual type of synchroscope, a saw-toothsweep pulse which will correspond to a signal other than the desiredone. Hence, a number of signals may appear simultaneously on the screenof the cathode ray tube insuperimposed position, making it impossible todistinguish the desired signal for evalua-tion.

My invention involves a novel arrangement by which' a single saw-toothsweep only is generated by the initial voltage rise in the ignitionsystem preceding the discharge of the spark plug at a time well beforethe desired portions of the corresponding signal are applied to' avertical beam deflection plate `of the cathode ray tube, thus providing,for the first time in the art, a practical and useful cathode ray tubeengine analyser in which cal and useful cathode ray tube engine analyserin which the saw-tooth synchronisingisweep pulse is generated by thevoltage rise in the ignition system itself.

It is a feature of my invention thaty the voltage rise for generatingthe saw-tooth sweep pulse may be taken from the high voltage secondaryof the engine ignition coil, through an attenuator connected to theterminal of the spark plug under test, while the signal impulse may betaken either from the high voltage secondary through an attenuator o"rfrom the low voltage primary of the engine ignition coil'. y

It is a further feature of my invention that the generation of asaw-tooth sweep pulse is prevented until a predetermined time intervalhas elapsed after the generation of a preceding saw-tooth sweep pulse,thus preventing the generation of saw-tooth sweep pulses by other than'the initial voltage rise in the ignition system preceding the sparkdischarge with corresponding multiple traces on the screen ofthe cathoderay` tube.

For the purpose of further explaining the foregoing and other featuresof my invention, reference is made to the following description of apreferred embodiment of my invention, when taken in connection with theaccompanying drawings, in which:

Fig. 1 is a general circuit diagram of the engine analyser of myinvention', in conjunction with an engine ignition system;

Fig. 2 is a series of illustrations of the pulses obtained at variouspoints in the circuit of Fig. l;

Fig. 3 is a series off illustrations of typical' waveforms at point A ofFig. 1 obtained with the deviceI of Fig. l, as portrayed on thescreenof' the cathode ray tube with the instrument on range Fig. 4 showstypical waveforms at point A of Fig. l, as portrayed on the screen ofthe cathode ray tube with the instrumenton range B; V

Fig. 5 shows typical waveforms at point' B of Fig. 1, as portrayed onthe screen of the. cathode ray tube with the instrument on range B, and

Fig. 6 shows typicalY waveforms at point B of'Fig. l, as portrayed onthe screen. of the cathode ray tube with the instrument on range C.

Referring to Fig. 1,2 the lelad wires from the cathode ray tube engineanalyser are connected to the engine ignition system by simple springclips or other suitablemeans, one connection being; made byy attachingthe attenuator lead wire l2, to the/highzvoltage secondary of theenginev ignition coil at-thetfsparlcplugrunder test, and the? attenuatorground wire 14 to any suitable point on the engine at ground potential.

The signal lead wire 16 to the vertical beam deflection plate 86 of thecathode ray tube 80, provided with a blocking condenser17 and preferablya filter comprising a radio frequency choke 18 and resistor 19, may beattached either directly to the low voltage primary of the ignitioncoil, for instance at the breaker points, point B of Fig. l, or totheterminal A on the attenuator, as hereinafter more fully explained. Bothforms of connection are ypreferred to enable a complete analysis of theignition system to be made.

The average ignition system in good condition is capable of producing avoltage rise of 20,000 to 25,000 volts, whereas the voltage necessary tobreak down the spark plug gap insulation is of the order of 8,000 toV12,000 volts depending on plug gap and the extent to which the mixtureis compressed. Hence, in a good ignition system there is a factor ofsafety of 100%, and this may be reduced considerably without affecting4the functioning of the motor.

On the other hand, an ignition system in poor condition has a very lowmargin of safety, hence, a load may be imposed by the attenuator toreduce the output voltage from the ignition coil to a point wheremal-functioning of the system is clearly visible on the screen of thecathode ray tube, as hereinafter more fully explained.

The attenuator generally designated at 20 consists of two capacityvoltage dividing networks which may be enclosed in a metal caseconnected to the engine analyser by a shielded line 21, enabling theattenuator to be placed near the spark plug under test and connected toit by a short lead wire 12.

The dividing network for reducing the input voltage for application tothe plates of the cathode ray tube when the signal input lead 16 isconnected to terminal A on attenuator 20 consists of condensers 22 and24 connected in series arrangement between the input lead from the sparkplug under test and ground. The signal voltage is taken from thejunction of the condensers 22 and 24 through a resistor 28 which acts asa terminating resistor for the linel16 to the vertical plate 86 ofcathode ray tube 80, preventing reflections of the input signal whichmight cause faulty operation of the device.

The constants of the attenuator 20, in particular the value of resistor38, and of condensers 22, 26, and 30, may be so chosen as known in theart to provide a suitable ignition system load to reduce the voltage inthe ignition system a substantial amount, preferably to a value greaterthan about two-thirds of its value without such a load. Under suchcircumstances, the load placed on the ignition system does not in anyway affect the performance of an ignition system which is in goodcondition, i. e. which has a 100% factor of safety, but will causemal-functioning of a system which has a lower factor of safety, andwhich is thus likely to break down in the near future.

A similar network is provided for reducing the input voltage foractuating the trigger shaper circuit consisting of condenser 30 andresistor 39 in series arrangement with either condenser 31, 32 or 33, aswitch 34 being provided to permit the switching of the condensers 31,32 and 33 to adjust the triggering voltage to the desired value foractuating the trigger Shaper circuit. A terminating resistor 36 isprovided for the shielded line 21.

The attenuator 20 reduces the very high voltage from the secondary ofthe ignition coil to a value suitable for actuating both the triggershaper circuit and the vertical deecting plate of the cathode ray tube80 without affecting the transient rise of ignition voltage.

If desirable, the amplitude of high frequency radiated signals such asthose inthe present day ignition systems used with high compressionengines may be reduced by the use of a low pass filter in series Vwiththe input lead 12 from the spark plug under test toI the attenuator 20,

The resistor 38, the resistor 39, and the condenser 26 constitute afilter suitable for such purpose.

The trigger shaper circuit, generally designated at 40, generates asingle sharply rising pulse which is substantially independent of therate of rise of the input voltage rise from attenuator 20, and is thenpositively prevented from generating a second pulse for a predeterminedtime thereafter, all as hereinafter more fully explained. Such a uniformsharply rising pulse is necessary for actuating the cathode ray tubesaw-tooth sweep generator circuit to produce consistent results undervarying degrees of malfunctioning of the ignition system under test, asthe characteristics of the input voltage rise from line 21 are notsuitable for actuating directly a cathode ray tube saw-tooth sweepgenerator circuit, since both the polarity and the rate of voltage risemay vary considerably depending upon the characteristics of the ignitionsystem.

The circuit of the trigger Shaper is that of a modied blockingoscillator, normally prevented from oscillating by means of a unilateralcurrent device such as diode 46 in the grid circuit of a pentode vacuumtube 48, said diode 46 acting to break the feedback loop between theplate 50 and grid 52 of the pentode vacuum tube 4S except when a signalof sufficient magnitude is applied to the plate of the diode 46. Aninput switch 42 permits switching the input line 21 to either terminal43 or 44 of the input of the trigger shaper circuit to enable tests tobe made on either positively or negatively grounded ignition systems.

lf a negative voltage rise is applied to switch 42 by the line 21 fromattenuator 20, switch 42 is moved to connect line 21 to terminal 43,supplying said pulse to terminal S6 of blocking oscillator transformer54 and to the plate 50 of the pentode vacuum tube 48 through the directcurrent isolation condenser 60. The windings of the blocking oscillatortransformer 54 are arranged in series aiding thus forming in effect asingle winding, with taps 57 and 53 at intermediate points on saidwinding between the end terminals 56 and 59 thereof, one of said tapsbeing connected by switch 62 in accordance with the polarity of theinput pulse to the cathode 53 of the pentode vacuum tube 48. If desired,said switch 62 may be mounted on a common shaft with switch 42. Sincethe taps 57 and are held at points of substantially constant potential,

a negative signal applied to the terminal 56 of the blocking oscillatortransformer 54 will result in a positive signal at the terminal 59 ofthe blocking oscillator transformer. Similarly, if a positive pulse isapplied to switch 42 by the line 21, and switch 42 is moved to connectline 21 to terminal 44 and thus to the terminal 59 of the blockingoscillator transformer 54 that is connected to the grid 52 of thepentode vacuum tube 48 through the diode 46 and blocking condenser 64, anegative pulse will appear at the other terminal 56 of the blockingoscillator transformer 54. Switches 42 and 62, then, permit the triggerShaper circuit to function in the same manner whether a ypositive or anegative voltage rise is supplied to the attenuator 20 by the spark plugunder examination.

The positive voltage rise appearing at terminal 59 of the blockingoscillator transformer will be transmitted to the grid 52 of the pentodevacuum tube 48 through diode 46 and condenser-64. I prefer to bias thecathode of the diode 46 to prevent triggering of the circuit by smallpositive voltage rises, such bias being obtained from voltage divider66. The voltage divider 66 is adjusted so that the wanted signals, i.e., those occurring in the ignition system immediately after the openingof the contact breaker points, are fed to the grid 52 of the pentodevacuum tube 48, but all other smaller signals occurring at other timesare prevented from passing to saidV grid. The pentode 48 is thusprevented from oscillating until the positive voltage at the plate ofthe diode 46 exceeds the positive voltage applied to the cathode of thediode 46 from the voltage divider` 66. When this occurs, the feedbackloop is completed through the diode 46 and the pentode vacuum tube 48begins oscillation, the blocking oscillator transformer 54 acting as atuned circuit incorporating a feedback loop from plate t) to grid S2 ofthe pentode vacuum tube 48. The oscillation of the pentode vacuum tube48 produces a first negative pulse at its plate 50, and such negativepulse is passed through blocking condenser 70 and diode 63 to the sweepgenerator circuit.

A second unilateral current device such as a diode 72 is connectedbetween the plate 50 of the pentode vacuum tube 48 and the cathode 53 ofthe tube l to provide the blocking action for said pentode. lt functionsin the following mannen-voltage changes at the plate of diode 72 whichmake the diode plate positive with respect to the diode cathode arerectified by the diode 72 and a positive voltage derived from therectfying process appears at the cathode of the diode 72. As thecathodes of the diode 72 and the pentode vacuum tube 43 are connectedtogether, the existing positive voltage at the cathode 53 of the pentodevacuum tube 48 is increased, this increase being suiiicient to cut offthe trigger circuit by preventing further flow of electron currentthrough the pentode vacuum tube 4S, The plate 50 of the pentode vacuumtube 48 is thereby raised to the level of the B-lsupply and is held atthat potential for a time determined by the time constants of thecathode and plate circuits of pentode 4d. These time constants are madeof such duration that the pentode vacuum tube d is rendered inoperativefor a period in excess of that during which any undesired potentialchanges at the plate of the tube may be expected, thus preventing thegeneration of output pulses by input voltage changes from line 2i withinsuch predetermined interval of time. I prefer that such interval be atleast 500 microseconds and preferably of the order of 1000 to 3000microseconds.

Fig. 2 illustrates the waveforms at various points in the triggershaping circuit. At Fig. 2a a typical waveform at the output of theattenuator is shown; other examples will be-seen in Figs. 3 and 4 asportrayed on the screen of the cathode ray tube. At time To on Fig. 2a,the distributor rotor gap breaks down and the rising voltage in theignition system secondary is transferred tothe high tension ignitioncable going to the spark plug to which the attenuator cable l2 isconnected. The voltage rise at this time exceeds the bias voltageapplied to the cathode of the diode d, which voltage is indicated by ahorizontal dotted line on Fig. 2a), and the pentode 4S startsoscillating, a negative output pulse being produced in approximately 0.2microsecond after diode lo beings to conduct, The output pulse frompentode i8 without diode 72 in the circuit is shown at To in Fig. 2b.After the initial negative pulse the plate voltage of the pentode 4Sswings positive in the usual blocking oscillator manner and were it notfor the large voltage change produced by the spark discharge at T2, theblocking oscillator oscillations would die away rapidly. The voltagechange due to the spark discharge produces a large positive swing at theplate of the pentode 48, and the latter half of the blocking oscillatorWaveform is repeated. At T3, the voltage at the input to the triggerShaper again exceeds the bias voltage on diode 45 and a second outputtrigger results.

ln Fig. 2c the erlect of the addition of diode 72 is seen. The initialpositive swing of the plate voltage of pentode 48 makes the plate of thediode 72 positive with respect to its cathode, and the diode 72conducts, thereby producing a positive voltage at the cathode. As thecathodes of the diode 72 and the pentode 48 are connected together, thispositive voltage is also applied to the cathode of the pentode 48,thereby reducing the plate current of pentode 43 and raising the platepotential towards B-lvoltage.` The second positive voltage rise at T2caused by the spark discharge raises the plate potential of pentode 48in a similar manner, in this case to the level of the appliedB-lvoltage. The time constants of the cathode and plate circuits arechosen to maintain the flow of current in pentode 48 at a level belowthat which is necessary to enable the pentode 43 to produec a gaingreater than unity for a predetermined period of time. lf the gain ofthe pentode stage is less than unity, the tube cannot oscillate and nooutput pulse can be produced.

Fig. 2d shows the output trigger pulse at the plate of the isolatingdiode 68.

This trigger shaping circuit is capable of producing a sharply risingnegative trigger pulse from a small change in input voltage and isimmediately thereafter automatically rendered inoperative, although thesubsequent changes in the input circuit are much greater in amplitudethan the small voltage change which produced the first trigger pulse. Bythis means, the radio frequency and other disturbances in the ignitionsystem are prevented from aifecting the action of the sweep generatorand clean sweeps, free from subsequent re-triggering, are produced.

Under conditions which would require that the pentode vacuum tube 48 beheld in an inoperative condition for longer than is possible by the useof a rectifyind diode in conjunction with pentode 48, a multivibratorsuch as is well known in the art may be triggered by the initialnegative output pulse from the triggershaper and a blanking pulse of anydesired duration produced by such multivibrator may be employed to cutoff or otherwise suppress the pentode vacuum tube 48.

The horizontal sweep generator circuits are of a conventional type wellknown in the art and are used to provide a saw-tooth sweep voltage pulsefor application to the horizontal beam deflection plates 82 and 84 ofthe cathode ray tube for the purpose of scanning a signal impulse suchas that provided by the rise and decay of the voltage of an engineignition system when such impulse is applied to the Vertical beamdeflection plate 86 of the cathode ray tube 80.

A gate generator circuit, also Well known in the art, is provided tosupply 'a voltage pulse of substantially square waveform which increasesthe brilliance of the cathode ray tube 80 only for the length of timenecessary to observe the desired signal trace, thus avoiding returntraces which` serve `only to confuse 4an observer. Such a gate pulse maybe obtained from the. screen grid 78 of the sweep generator tube 76.

The output pulses of both the sweep amplifier and the gate generatorcontrol the cathode ray tube through its associated circuit componentsin the usual manner, the sweep generator and ampliers providing thesaw-toothed pulse to be applied to the horizontal plates 82 and 84 ofthe cathode ray tube 80, enabling observation of the signal voltage asdirectly applied to the vertical plate 86 of the tube 80, -while thegate generator provides a square pulse which is applied to the beamintensity control grid 89 of the cathode ray tube 80. In the preferredembodiment shown, the horizontal sweep generating multivibrator consistsof the triode 90, the pentode 76 and the diode 101, the diode 68 actingas a switch isolating the trigger Shaper circuit 40 from saidmultivibrator except when a large negative voltage is present at thecathode of the diode 68, that is, during the production of a trigger bythe trigger Shaper;

In the absence of a 'trigger from the trigger shaper, the triode 90 isquiescent, the grid bias obtained from the junction of the resistors 71and 72 being sufficient to completely cut off the Lflow of plate currentin said triode. Under these conditions, the plate 103 of the triode 90has a positive potential equal to that of the B+ supply. The cathodecondenser 73 increases the gain of the triode 90 whenl platecurrentstartsI to flow by preventing the degeneration which. would occur if thecathode resistor 72 were not by-passed for signal currents. The pentode76 then passes maximum plate current, being limited only by theresistors 107, 108, and 109 in series with the screen grid 78 and by theresistor 91 in series with the plate 99. Because of such high platecurrent flow, the plate potential of pentode 76 is only 'a few voltsabove ground. The grid 100 and the screen grid 78 of pentode 76 act aslthe grid and plate respectively of a triode vacuum tube. The actualplate 99 of' the pentode plays no part in the action of themultivibrator formed by the triode l90 and the triode formed by the grid100 and the screen grid 78 of the pentode tube 76. The plate 99, is,however, connected electronically to the other electrodes in the tube,and its potential is controlled by the action of the grid and screengrid of the tube. The diode 101 and resistor 102 maintain the pentodegrid 100 at a constant potential a few volts below ground during thequiescen-t period. i

On the arrival of a sharp negative trigger pulse from the triggershaperthrough suitable condensers selected by the switches 92 and 94-atthe grid 100 of the pentode 76, the plate current through the tube isdecreased, allowing the screen grid 78 to rise to a higher voltage. Thisvoltage rise is transferred through the resistor 110 and the condenser106 to the grid 104 of the triode 90. This reduction of grid bias on thetriode 90 results in a flow of plate current through the tube `and `theplate potential falls, the fall in potential being transferred to thegrid 100 of ,the pentode 76 through one of the condensers 113, 114, or115 as selected by the switch 94, thereby reinforcing the negativetrigger voltage and still further decreasing the flow of plate currentthrough the pentode 76` The action is regenerative and results in thecessation of plate current ow in the pentode 76 and the passage of alarge plate current in the triode 90, such action preferably beingcomplete in approximately 0.1 micro-second after the Varrival of thetrigger pulse.

At the end of the regenerative action, one of the condensers 113, 114,115 is charged and so produces -a large negative voltage on the grid 100of `the pentode tube 76. Then, until one of the condensers 113,114, or115 has discharged through resistor 102, no current can flow in thepentode 76, and the multivibrator remains in the described conditionwith the triode 90 conducting and the pentode 76 cut-off. The dischargeof the condenser 113, 114, or 115 to a potential which will permitcurrent to flow in the pentode tube 76 will occur after a period of timedetermined by the capacity of the' condenser and the value of theresistor 102. Switch 94 permits selection of a condenser of appropriatevalue for the time interval desired.

The triangular sweep voltage is produced as follows: While condenser113, 114, or 115 is discharging, no current flows in the pentode 76 andthe plate 99 tries to rise towards B+. However, this rise cannot takeplace until the condenser 93, 95, or 97 selected by switch 98 hascharged positively, and the potential at the plate 99 of the pentoderises exponentially at a rate determined by the capacity of thecondenser selected by switch 98 and the value of resistor 91. The rateof movement of the spot of light across the screen of the cathode raytube 80 is controlled by selection of the appropriate condenser 93, 95,or 97. The time 4during which the spot is permitted to move across thecathode ray tube screen is controlled by selection of the appropriatecondenser 113, 114, or 115; and during this period, the spot of light isincreased4 in intensity by the application of a rectangular positivepulse from the screen grid 78 of the pentode through switch 96 andcondenserxSS `to the grid 89 of the cathode ray tube 80.

During the period of discharge of condenser 1'13, 114, or 115 the screengrid 78 of the pentode 76 will remain at a potential determined by thevalues of the resistors 107, 108, and 109 in series with resistors 105and 110; the whole potential divider being connected between the B+supply and ground. This results in the` production of a rectangularpositive pulse of the same time duration as the discharge time of thecondenser 113, 114, or 115: By tappings between resistors 107, 108, and109 the amplitude of the rectangular pulse may be suitably chosen forthe sweep rate involved and by inverting this positive pulse in a vacuumtube amplifier `and applying the resulting negative pulse through aswitch diode to the suppressor grid of the pentode 48, said pentode maylbe prevented from functioning for a period of time determined by thetime constant of the condenser connecting the plate of the switch diodeto the suppressor grid and a resistor connected inthe lead between thesuppressor grid and ground, thus providing a blocking pulse from themultivibrator, an alternative to the blocking p ulse means ashereinbefore described.

When the negative voltage on the grid 100 of the pentode 76 has fallento a Value 4at which plate current can llow in the pentode 76, thevoltage at the screen grid 78 starts to fall, as does the voltage at theplate 99. The fall in voltage at the screen grid 78 is transferred tothe grid 104 of the ltriode 90 through the condenser 106 and theresistor `110, resistor 110 being included to complete the potentialdivider between B+ and ground as described above, while the condenser106 prevents the slowing down of the rate of transference of the pulsebetween the screen grid 78 and the triode grid 104. Condenser 116 isconnected across the resistor 107 for a similar reason.

The fall in voltage fed to the grid of the triode causes a reduction ofplate current in that tube, with a consequent rise in voltage at theplate 103. This voltage rise is transferred to the grid ofthe pentode 76and a reversal of the previously described regenerative action takesplace, resulting in cessation of plate current in the triode 90, theflow of maximum plate current in the pentode 76, and the discharge ofcondenser 93, 95, or 97 through the pentode tube 76. The circuit hasthus reverted to its original condition prior to the arrival of atrigger pulse from the trigger shaper and remains in that conditionuntil another pulse is produced by the trigger shaper. The discharge ofcondenser 93, 95, or 97 through the pentode tube stops the movement ofthe spot across the cathode ray tube screen, and the spot is returnedvery rapidly to its original position on the screen. As no rectangularpositive pulse is produced at the screen grid of the pentode 76 duringthis reversal action the beam of electrons in the cathode ray tube isnot intensified and the return trace is not visible.

As hereinbefore stated, the voltage `at the plate 99 of the pentode tube76 rises exponentially towards B+. By suitable choice of values ofcondensers 113, 114, and which determine the duration of this period,and of condensers 93, 95, and 97 which determine the rate of rise ofvoltage during this period; use is made only of the early part of theexponential rise at the plate of the pentode 76; this rise beingreasonably linear. This approximately linear rise may be made completelylinear, as now will be described.

The rising voltage at the plate of the pentode 76 is transferreddirectly to the grid of the triode 117 which is connected `as a cathodefollower having a gain of approximately unity. The resulting signalappearing at the cathode is transferred through condenser 121 to thehorizontal decction plate 84 of the cathode ray tube 80. The voltagerise so applied to the deection plate 84 is exponential in form. Thesignal at the cathode of the triode 117 is also transferred throughcondenser 123 and resistor 122 to the grid of the triode 130. The rateof rise of voltage at the grid 129 of triode 130 is slowed down by theseries resistor 122, as the stray and `tube capacities at the grid 129have to charge through resistor 122. This effect is most pronounced atthe start of the rise of the exponential signal at the grid, andtherefore the start of the voltage rise is slowed down in relationshipafa-'411,069

' 9 with the later, more slowly rising portion of thexi'ncom'l ingsignal.

To allow the grid of triode 130 to be conductivelyv con` nected to thecathode of triode 117, the resistor 126 is made large to raise thecathode of triode 130 to a suitable grid bias level. At the beginning ofthe voltage rise at the grid of triode 13E), the bias voltage is suchthat the transconductance of the tube is low, As the voltage rises atthe grid, the bias is reduced and the stage gain is increased. These`two effects product a hyperbolic voltage fall at the plate of thetriode 130. The shape of this hyperbolic fall may be controlled by thecorrect choice of condenser 123 which modifies the effect of the seriesresistor 122 and of condenser 127 which controls the rate of rise ofvoltage at the cathode of triode 130; and therefore the transconductanceat dierent portions of the signal from triode 117.

By suitable choice of condensers 123 and 127,n the hyperbolic voltagefall applied through condenser 125 to the horizontal deflection plate 82of the cathode ray tube may be made of such shape that when combinedwith the exponential voltage rise applied through condenser 121 to thehorizontal deflection plate 84 of the cathode ray tube the spot of lightis made to travel at auniform rate across the screen of the cathode raytube.

The vertical and horizontal positions of the spot on the cathode raytube screen are controlled by variable resistors 140 and 141; variableresistance 142 allows the voltage on the final anode S7 of the cathoderay tube to be set for optimum overall focus; and variable resistances153 and 156 control the focus and brilliance of the spot respectively.

By observation of the rate of rise, amplitude, and character of thewaveforms of the ignition system voltage rise as portrayed on the screenof the cathode ray tube, and by analysis and comparison of suchwaveforms with normal waveforms, the condition of the various ignitionsystem components may be easily checked. Furthermore, the condition ofvalves and rings may be determined, as the amplitude of the voltage riseis affected by the compression. Since faulty rings will g-ive aconstant, though low, compression from stroke to stroke, and faultyvalves will give a variable compression from stroke to stroke due tovariations in seating, it may be determined which is at fault, and inwhat particular cylinder the trouble arises, all of such informationbeing obtained without the use of an accessory drive on the motor toprovide a triggering or synchronizing Voltage.

If desired, the engine analyser of my invention may be used to measuredirectly the compression ratio of a cylinder, since the amplitude of thevoltage rise in the ignition system secondary has been shown by PaschensLaw to be directly proportional to the pressure of the mixture in thecylinder, the electrode shape and gap of the spark plug, and to a lesserextent to such factors as the temperature, and the chemical compositionof the explosive mixture. Hence by the use of a calibrated engineanalyser to measure the voltage rise at the spark plug of the cylinderunder test, assuming the spark plug to be in new condition, thecompression ratio may be read directly on the screen of the cathode raytube, since for practical purposes, the temperature and composition ofthe explosive mixture may be ignored.

The cathode ray tube engine analyser is preferably provided with threeranges, A, B and C, the desired range being selected by range switch 92,94, 96 and 98, which switches circuit components in the sweep generatorand gate circuits, as is well known in the art, to provide the properlength of sweep and gate waveforms for the range desired.

Range A comprises the highest sweep speed, permitting the examination ofthe characteristics of the spark plug discharge, its speed being highenough to show the high frequency oscillations set up by the sparkdischarge.

Range Br comprises a slower sweepV speedl and permits` the examinationof the entiresignal trace from the spark plug under examination, fromthe initial: rise of voltage in the secondary ofthe ignition coil toIthe. return of the system to conditions for beginningv of the cycle oftheA next sparkplug to be tired.

Fig. 4 shows typical waveforms at point A of Fig. l. on range B, andFig. 5 typical waveforms at point B; of Fig. 1 also on range B.

Range C comprises the slowest sweep speed and permits-observation ofthewaveforms accompanying two or more sparks as said sparks follow.eachother in the firing order of the engine. This range permitsexamination of the period duringV which the. contact breaker points areclosed prior to the spark in each cylinder. Observation of thedistancebetween successiveA waveforms as seen on the cathode ray tubescreen, and they proportion of this distance during which the points areclosed, gives the closed period in degrees of distributor shaftrotation. A simple nomogram may be provided with the instrument tofacilitate the calculation.

In addition, use of range C notmerely confirmsy the presence ofcross-tiring in the engine as. indicated by ranges A and B, but enablesthe operator to determine which cylindery is cross-firing, and whichother cylinders are being affected. Indications of irregularities in theshape of the distributor cam, looseness in the spark advance plate, wearin the distributor shaft bearing, and faulty contact breaker action maybe observed on ranges A and B, but are confirmed and precisely locatedon range C.

Typical examples of the waveforms taken from point B of Fig. l as seenon the cathode ray tube with the instrument on range C are shown in Fig.6.

From the foregoing description it will be seen that the engine analyserof my invention as herein described permits tests of ignition systemsand their associated components as well as compression conditions to bemade without complicated mechanical attachments, while the engine isunder operating conditions. Such tests may be simply and easily made bya person without technical knowledge by a simple comparison of theobserved pattern with illustrations of typical patterns showing variousengine faults.

I claim:

l. An internal combustion engine analyser comprising a cathode ray tubehaving vertical and horizontal beam dellecting means, horizontal sweepmeans for said cathode ray tube, signal actuated trigger means producinga trigger pulse for actuating said horizontal sweep means, triggerblocking means rendering said signal actuated trigger means itselfinoperative for a predetermined interval of time after said triggermeans has been actuated to produce a trigger pulse, and means forapplying a signal to said trigger means and to said vertical beamdeecting means.

2. An engine analyser according to claim l in which said signal actuatedtrigger means includes an oscillator having vacuum tube means, and saidblocking means includes a unilateral current device arranged andconnected to said oscillator vacuum tube means to cut olf said vacuumtube means by preventing flow of electron current therein.

3. An engine analyser according to claim l in which said signal actuatedtrigger means includes an oscillator having vacuum tube means, and saidblocking means includes a multivibrator arranged and connected to saidvacuum tube means to cut off said vacuum tube means by preventing ow ofelectron current therein.

4. An internal combustion engine analyser comprising a cathode ray tubehaving vertical and horizontal beam deflecting means, horizontal sweepmeans for said cathode ray tube, signal actuated trigger means producinga trigger pulse for actuating said horizontal sweep means, saidtriggermeans including blocking oscillator meanswith'a feed-v backcircuit having means arranged and connected therein to break saidfeedback circuit and prevent operationof said oscillator means exceptwhen a signal is applied to said trigger means.

5. An internal combustion engine analyser as claimed in claim 4 in whichsaid means arranged and connected to break said feedback circuitincludes a unilateral current device.

6. An engine analyser according to claim 5 in which said oscillatorfurther includes bias voltage means connected to said unilateral currentdevice to prevent operation of said oscillator except when a signal lofgreater amplitude than said bias voltage is applied to said triggermeans.

7. An internal combustion engine analyser comprising a cathode ray tubehaving vertical and horizontal beam deecting means, horizontal sweepmeans for said cathode ray tube, signal actuated trigger means producinga trigger pulse for actuating said horizontal sweep means, triggerblocking means actuated by said signal actuated trigger means renderingsaid signal actuated trigger means itself inoperative for apredetermined interval of time after said trigger means has beenactuated to produce a trigger pulse, and means for applying a signal tosaid trigger means and to said vertical beam deecting means.

8. An internal combustion engine analyser as claimed in claim 7 in whichsaid signal actuated trigger means includes blocking oscillator meanswith a feedback circuit having means arranged and connected therein tobreak said feedback circuit and prevent operation of said oscillatormeans except when a signal is applied to said trigger means. v

9. An internal Vcombustion engine analyser as claimed in claim 8 inwhich said means arranged and connected to break said feedback circuitincludes a unilateral current device.

References Cited in the file of this patent UNITED STATES PATENTS2,358,545 Wendt Sept. 19, 1944 2,367,728 Mahoney, Jr Jan. 23, 19452,431,766 Miller et al. Dec. 2, 1947 2,449,801 Bias et al. Sept. 21,1948 2,450,164 Ramsay Sept. 28, 1948 2,460,112 Wright et al. Jan. 25,1949 2,466,924 Bradford et al Apr. 12, 1949 2,467,834 Lasher, Jr. Apr.19, 1949 2,480,878 Rea Sept. 6, 1949 2,496,283 Gall Feb. 7, 19502,496,970 Wertz Feb. 7, 1950 2,522,124 Klute Sept. 12, 1950 2,621,306Varela et al Dec. 9, 1952

